Lance pipe for the injected oxygen in steel making



SUNAO NISHl Dec. 20, 1966 LANCE PIPE FOR THE INJEC'I'ED OXYGEN IN STEEL MAKING Filed July 8, 1963- FIG.

FIG. 2

United States Patent LANCE PIPE FOR THE INJECTED OXYGEN IN STEEL MAKING Sunao Nishi, 454 Ieno Machi, Nagasaki-shi, Japan Filed July 8, 1963, Ser. No. 293,393

Claims priority, application Japan, Feb. 4, 1963,

2 Claims. (Cl. 138-141) This invention relates to a lance pipe applicable for the direct injection of the oxygen in the steel making operation.

The practice of introducing a lance pipe through a peephole provided in the furnace door and inserting slantwise the pipe, through an atmosphere of high temperature in the furnace, to a point of a length from 500 to 1000 mm. from its tip into a puddle of slag and steel bath is well known to those familiar with the steel making process. It is also a recognized fact that although the lance pipe undergoes a rise in its temperature, said lance pipe will not reach a temperature equal to that of the furnace atmosphere by virtue of the cooling effect due to the passage of high pressure oxygen at a high velocity whereby the lance pipe is prevented from melting. However, the temperature of the part of the pipe length from 2 to 3 meters in the furnace will reach a high temperature from 900 to 1200 C. On the other hand, the steel has a property such that it will burn with a bluish glow when it is heated at a temperature of about 900 C. even in an atmosphere of pure oxygen. As a consequence, a steel pipe will commence to burn from its tip or infrequently from an intermediate point, whereby the length of said pipe is consumed at a rate as low as 500 mm. and up to as much as 2000 mm. per minute. Furthermore, the portion of the pipe exposed directly to the furnace atmosphere loses its wall thickness due to the occurrence of scaling which contributes also to further consumption of the lance pipe.

Even though the direct steel bath blowing process can afford a high etficiency and lesser damage, its practical application has been difiicult because of the severe consumption of the lance pipe per se.

For the purpose of preventing the lance pipe from being consumed, it has been proposed to shield the direct radiation of the furnace heat so as to maintain the pipe at a low temperature by coating the exterior surface thereof with a refractory sleeve or by providing a thick partition wall of a refractory material. However, the sleeved pipe has various disadvantages such that due to the smaller specific gravity of the refractory material than that of the slag and molten metals, the insertion of the sleeved pipe into the bath is diflieult and the tip of the pipe unavoidably floats on the molten metal and slag, thus causing the wall and ceiling of the furnace to be disturbed by the direct blast of the oxygen thereonto. Also, the sleeved pipe is easily damaged and becomes so heavy that handling of the pipe is difficult. Furthermore, the above-mentioned countermeasures cannot be deemed to be economical due to the cost of the refractory material such as fire brick and the damages normally encountered prior to their setting.

Therefore, an essential object of the present invention is to provide an improved lance pipe, the material consumption, lightness and solidness, and handling of which are, respectively, less, very excellent, and easier than those of the conventional lance pipe.

Patented Dec. 20, 1966 The above and other objects of this invention have been attained by not only shielding the furnace heat from the pipe, but also converting the pipe Wall into an antioxidation state through the impregnation of an appropriate amount of aluminum thereinto, and furthermore by providing a refractory film of not too great thickness on the outer surface of the treated pipe to shield the oxygen and the high furnace heat from coming into direct contact with the pipe metal and providing a thin refractory film on the interior surface of the pipe to avoid the direct contact of oxygen and metal. The manner in which the foregoing as well as other objects and advantages of the present invention may best be achieved will be understood more fully from a consideration of the following description of one embodiment of the invention, taken in connection with the accompanying drawing, in which:

FIG. 1 is a cross sectional view of the lance pipe taken at a right angle to the longitudinal axis of the pipe, and

FIG. 2 is a partial cross sectional view of the forward end of the lance pipe in the state of blowing oxygen.

Referring to FIG. 1, the lance pipe comprises a unimpregnated part 3 of the base metal, a Fe-Al allow layer 4 formed by diffusing aluminium onto the interior wall of the pipe, 2. Fe-Al alloy layer 2 formed by diffusing aluminium onto the exterior wall of the pipe, a refractory film 5 of a low softening point coated on the Wall 4, and a porous refractory film 1 of substantial thickness on the layer 2. FIG. 2 shows the state of the forward end of the lance pipe of the present invention at the time of the oxygen injection during a smelting operation wherein numeral 6 indicates the manner in which the refractory film 5 outflowing under the influence of the oxygen blast envelopes the end surface inclusive of the base metal 3 exposed by the melt consumption and numeral 7 shows the state of the slag adhered on the thick porous film 1. The adhering layer 7 is shown on a reduced scale for convenience, but is substantially much heavier in practice than shown.

The method of aluminium impregnation is left to choice. The concentration of aluminium penetrating to a depth of 0.1 mm. from the surface must, however, be from 28- 33% for the interior pipe wall 4 and from 18-26% for the exterior pipe wall 2, and in both cases, the concentration should taper ofi gradually and blend naturally into the base metal 3. The depth of the impregnated layers 2 and 4 should be such that the part of the base metal 3 is at least between /z /2, of the total pipe wall thickness.

The limitation of the aluminium concentration above indicated is established on the basis of factual deductions wherefrom it has been found that for the interior layer 4 a concentration of less than 28% induces greater lance consumption and also a concentration greater than 33% would again cause great consumption. It has been found that the forward tip of the interior wall is subjected to a severe attack by oxygen, whereby the iron, negligible as it may be, commences to burn in the case of aluminium concentration less than 28% and the alloy layer would start to melt, in the case of aluminium concentration over 33%. This fact is considered to be fairly correct based on the experiments carried out in connection with wires (No. 10 gauge) having respectively, impregnated aluminium layers of various concentrations. That is to say, it was found that a wire of a high aluminium concentration, when it is subjected to the direct blowing of oxygen alone after being heated with an oxygen-acetylene flame, cools immediately whereas a wire of a low aluminium concentration burns, giving off a small display of spark.

If the aluminium concentration in the layer 2 on the exterior surface is excessive, the melting point of the layer w'dl decrease and the layer will start to melt and disintegrate under the furnace heat, whereas, on the other hand, an insufiicient concentration tends to invite scaling and burning at the forward tip end where it is most susceptible to consumption. Therefore, the consumption will tend to become great with either excessive or insuflicient aluminium concentration.

It is desirable to use an impregnated layer of greatest thickness. Therefore, a pipe wall which is composed in its all parts of Fe-Al alloy would be ideal. However, this pipe is liable to be subjected to breakage problems due to the brittleness of the alloy. As a prospective measure against the breakage, the un-impregnated base metal 3 of a thickness between /z- /s of the thickness of the pipe wall should remain, but such remaining portion should be preferably within the upper limit, because the base metal 3 is readily damaged at its extreme tip by the oxygen gas.

The refractory film 5 provided on the interior surface of the pipe should be composed preferably of at least one kind of refractory material and a ceramic material of such a low melting point that'at least about 30% of the ceramic material will be transformed into a glassy state and commence to flow at a temperature of about 800 C. Alternatively, the refractory film 5 can be provided on the interior surface of the pipe by a process which comprises mixing well a composition having been made to promote transformation thereof into a glassy state by the addition of an element like borax thereto with a water glass diluted to a density between -25-35 B. so as to form a fine grain paste applying the paste onto the interior surface of the pipe to form a thin filim of about 0.1 mm. thickness, subjecting the applied film to a quick drying at a temperature below 100 C., and then calcining the dried film at a temperature above 300 C. The compositional structure of the fi-lm 5 should-be as fine and thin as possible in order to prevent the metal surface of the pipe interior from being contacted by the oxygen and to permit optimum transmission of the cooling effect of the oxygen to the pipe wall, thus restricting the temperature rise in the pipe.

The temperature at the interior wall of the pipe ranges from 900 to 1000 C. which is very low when compared with the furnace temperature. However, the refractory film 5 having a W softening point will be transformed, before said temperature is established at the interior W311i of the pipe, into a semi-molten state having a glass-like property thus causing a part of the film in the vicinity of the forward tip end of the pipe to flow out by the blast action of the injected oxygen, with the flowing material serving not only to prevent the oxygen from coming into contact with the metal surface of the pipe, but to provide a protective coating over the metal surface exposed at the tipmost cut-off point of the pipe. This exposure results from consumption, and particularly for preventing the burning-off of the part of the tin-impregnated base metal 3, which part is most susceptible to the ravaging effect of the oxygen gas. On the other hand, the fillm on the interior surface of the pipe, by virtue of its thinness and low softening point, would not be separated by the thermal expansion and contraction of the base pipe.

The film 1 on the exterior surface of the pipe functions as a shield against the furnace heat as Well as a base for slag adhesion. Since the coefiicient of thermal expansion of a metal is always substantially greater than that of a refractory material, it follows that their separation would naturally occur more readily. Although the refractory material on the outer surface of the pipe will practically never be separated under temperature rise conditions because of the uniform pressure exerted thereon from the innerside, under a condition of temperature decrease, separation takes place readily when the temperature falls below the softening point of the refractory material. The cause for this separation is due to the substantially lower magnitude of contraction in the impregnated layer after hardening thereof than that of the contraction in the metal. This undesirable disadvantage has been eliminated by use of a porous film which has proven to be effective even after repeated usage.

According to the present invention, the major part of the outer surface of the pipe is first applied with a film consisting basically of refractory material of a highest softening point and of compositional nature resistive to vitrification even when it is subjected to the direct influence of the furnace heat. Then, the fihn coating is applied to a thickness of less than 2 mm., with a paste temperature below C. and calcined at a temperature above 300 C. The film prepared by the process as described above will retain its finely perforated characteristic before a high heat application thereto. The film, by virtue of its porosity, maintains a proper relationship to the thermal expansion and contraction of the metal portion of the pipe through the aligning function afforded i by the resultant action of minor thermal expansions and contractions of the plural fine pores.

a heat insulator capable of restricting the transmission of furnace heat to the metal as well as a base for. slag adhesion.

It is obvious that a refractory material provided on the outer surface and having a high softening point is selected with the object of preventing the reduction of the porosity through its vitrification under a high temperature. The admixture of a carbonate is adapted to promote and maintain the porosity of the film through the generation of carbonic acid gas therefrom. The limita-. tion of the film thickness to less than 2 mm. is established in order to permit rapid drying,,prevent the deterioration of the separability of the film due to any mechanicalshock, and limit the weight increase of the pipe to a minimum. The reason for preparing the refractory coating in the form of a paste with water glass having a density of 25-35 B. is to expedite the rapid drying of the water glass as well as insure the highest possible strength of the film. It has been ascertained that when the density of the water glass is greater than 35 B., the drying character-istic is poor and a fully satisfactory surface fil-m cannot be obtained because of the loss of the water glass before the refractory grains have suflicient time to become than 25 B. of the water glass results in a film of such physical strength as would not be capable of withstand ing any rough handling. Furthermore, the drying of the coated paste at a temperature above 100 C. causes foaming of the water glass and fracture of the film. Consequently, drying at a temperature above 100 (1., though quick drying may be desirable, only leads to absolutely unsatisfactory results. It is also very impartant to note that the layer must be subsequently calcined at a temperature above 300 C., because the surface filrn will, unless further treated, reabsorb moisture and soften at room temperature. The surface film thus treated will cause the water glass to lose completely its moisture-absorbability, and, although its physical strength will be reduced slightly, it will be found that the film thus treated will not foam even when it is put into a furnace of 1000 C. immediately after having been immersed in water for 24 hours.

Also, its surface layer will not separate even when itis Consequently, the film will not strip or separate from the underside of the pipe. This porous film is therefore suitable for serving as.

thrown into water after having been heated in a furnace to 1000 C.

An example of a practical embodiment of the present invention is given hereinafter to show the compositional makeup of the exterior and interior coatings and their depths and concentrations.

Raw pipe: Mm. Inside diameter 22.3 Wall thickness 2.3 Length 6,800

Aluminium layer-Impregnated according to the method as prescribed for powdered Fe-Al alloys:

Interior surface, layer depth 0.65 mm. Surface Aluminium concentration 31.58% (ml-Iv. 540). Exterior surface, layer depth 0.60 mm. Surface Aluminium concentration 22.37% (mHv. 400). Interior coating:

The pipe as obtained according to the foregoing composition was practically applied in a 150-ton basic open hearth furnace and it was confirmed that the rate of the lance consumption was 30 mm./min. during the smelting period and 74 mm./min. during the refining period. In the case of an untreated pipe tested in the same furnace under the same conditions the rate of the lance consumption was 546.6 mm./min. during the smelting period and 942 mm./min. during the refining period. Accordingly, the lance pipe prepared under the present invention demonstrated superior qualities.

The principal feature and application of the present invention has been clarified in the above explanation, but since it is to be noted that the specific embodiments given herein are cited for the purpose of illustration, various modifications are conceivable without departing from the spirit and scope of the appended claims of the present invention.

What is claimed is:

1. An oxygen injection lance pipe for steel making, comprising a calorized steel pipe consisting of an unimpregnated base metal and aluminum diffused in the interior and exterior wall parts of the pipe, the average concentration of the aluminum within the thickness of the interior and exterior wall parts of the pipe to a depth of 0.1 mm. being from 28-33% and from 18-26% respectively, a film consisting of a composition comprising at least one kind of refractory material and a ceramic material having a property capable of being transformed into a vitrified and fluid state at a low temperature on the aluminum diffusion into the interior wall part and having a thickness of 0.1 mm., a film consisting of a composition comprising at least one kind of refractory material having a high melting point and a small quantity of a carbonic acid gas generating material of carbonate type on the aluminum diffused into the exterior wall part for promoting and maintaining the porosity of the film and having a thickness of from 0.9-1.2 mm., said films including water glass of a density of 25-35 B. and said base metal being between one-half and two-thirds of the total thickness of the pipe wall.

2. An oxygen injection lance pipe for steel making, comprising a calorized steel pipe consisting of an unimpregnated base metal and aluminum diffused in the interior and exterior wall parts of the pipe, the average concentration of the aluminum within the thickness of the interior and exterior wall parts of the pipe to a depth of 0.1 mm. being from 28-33% and from 18-26% respectively, a film consisting of a composition comprising at least one kind of refractory material and a ceramic material having a property capable of being transformed into a vitrified and fluid state at a low temperature on the aluminum diffusion into the interior wall part and having a thickness of 0.1 mm., a film consisting of a composition comprising at least one kind of refractory material having a high melting point and a small quantity of a carbonic acid gas generating material of carbonate type on the aluminum diffused into the exterior wall part for promoting and maintaining the porosity of the film and having a thickness of from 0.9-1.2 mm., said films including water glass of a density of 25-35- B., said base metal being between one-half and two-thirds of the total thickness of the pipe wall, and said film on said interior wall part contains borax adapted to promote its vitrification.

References Cited by the Examiner UNITED STATES PATENTS 2,311,138 3/1939 Swartz l38145 XR 2,745,797 5/1956 Long 138-145 XR 2,843,646 7/1958 Conant 138-145 XR 3,036,929 5/1962 Kawashima et al. 138145 XR 3,044,499 7/1962 Frerich 138143 3,173,451 3/1965 Slayter 138145 OTHER REFERENCES Sears, Roebuck & Company catalog publication,

Spring & Summer 1959, pp. 1118 and 1119; copy in group 430, 181-61.

LAVERNE D. GEIGER, Primary Examiner.

H. K. ARTIS, Assistant Examiner. 

1. AN OXYGEN INJECTION LANCE PIPE FOR STEEL MAKING, COMPRISING A CALORIZED STEEL PIPE CONSISTING OF AN UNIMPREGNATED BASE METAL AND ALUMINUM DIFFUSED IN THE INTERIOR AND EXTERIOR WALL PARTS OF THE PIPE, THE AVERAGE CONCENTRATION OF THE ALUMINUM WITHIN THE THICKNESS OF THE INTERIOR AND EXTERIOR WALL PARTS OF THE PIPE TO A DEPTH OF 0.1 MM. BEING FROM 28-33% AND FROM 18-26% RESPECTIVELY, A FILM CONSISTING OF A COMPOSITION COMPRISING AT LEAST ONE KIND OF REFRACTORY MATERIAL AND A CERAMIC MATERIAL HAVING A PROPERTY CAPABLE OF BEING TRANSFORMED INTO A VETRIFIED AND FLUID STATE AT A LOW TEMPERATURE ON THE ALUMINUM DIFFUSION INTO THE INTERIOR WALL PART AND HAVING A THICKNESS OF 0.1 MM., A FILM CONSISTING OF A COMPOSITION COMPRISING AT LEAST ON EKIND OF REFRACTORY MATERIAL HAVING A HIGH MELTING POINT AND A SMALL QUANTITY OF A CARBONIC ACID GAS GENERATED MATERIAL OF CARBONATE TYPE ON THE ALUMINUM DIFFUSED INTO THE EXTERIOR WALL PART FOR PROMOTING AND MAINTAINING THE POROSITY OF THE FILM AND HAVING A THICKNESS OF FORM 0.9-1.2 MM., SAID FILMS INCLUDING WATER GLASS OF A DENSITY OF 25-35* BE''. AND SAID BASE METAL BEING BETWEEN ONE-HALF AND TWO-THIRDS OF THE TOTAL THICKNESS OF THE PIPE WALL. 